The invention relates to a two-stroke engine with controlled pneumatic injection.
Multi-cylinder two-stroke engines generally comprise, associated with each of the cylinders, a housing called "crankcase-pump" communicating with one of the ends of the combustion chamber of the cylinder and feeding fresh gases into the cylinder, via at least one duct and a transfer opening. The piston which reciprocates in the cylinder also provides suction and compression of the fresh gases in the crankcase-pump. An intake valve disposed on the crankcase-pump allows fresh gases to be fed into the crankcase when the piston moves in the direction opposite the crankcase, the fresh gases then being compressed and causing closure of the valve, when the piston moves towards the crankcase. When the corresponding openings of the cylinder are freed by the piston, fresh gases are fed into the cylinder through the transfer ducts and openings and cause sweeping with fresh gases for replacing the burnt gases which are discharged through exhaust openings generally disposed in staggered fashion with respect to the transfer openings. The piston moves away from the crankcase so as to compress the gases contained in the cylinder. The ignition and combustion of the air and fuel mixture then produce the drive stroke of the piston towards the crankcase.
In the case of a multi-cylinder engine, pneumatic fuel injection into a first cylinder is provided by using the pressure of the fresh gases inside the crankcase-pump of a second cylinder whose piston moves with an angular shift with respect to the piston of the first cylinder, considering the rotation of the crankshaft passing in the axial direction through the assembly of crankcase-pumps of the engine.
Generally, the pressurized air used for injection in a cylinder comes from the crankcase-pump of a second cylinder whose delay, in so far as the rotation of the crankshaft is concerned, may be 120.degree., in the case of an engine with three, six, . . . three n cylinders or else 90.degree. in the case of an engine with four, eight, . . . four n cylinders with respect to the cylinder in which the injection takes place.
Devices have also been proposed for controlling the injection of the carburetted mixture and in particular devices for controlling the beginning of introduction of this carburetted mixture at the end of scavenging of the cylinder of the engine with fresh air.
These devices may be formed by an automatic valve, a controlled valve, a rotary valve or else by an opening formed in the second cylinder from which the injection takes place, cooperating with the skirt of the corresponding piston.
Generally, no control or check of the injection takes place directly at the output of the crankcase-pump, at the level of an opening in this crankcase-pump to which the duct for connection to the first cylinder is connected.